The present invention relates to a packaging structure for a microwave circuit, and more particularly to a packaging structure including a microwave circuit module or microwave IC module.
As well known, the wavelength of a microwave or millimeter wave region is short and, therefore, it is difficult to design a circuit arrangement including transmission lines while suppressing discontinity on the lines to a low level and ensuring isolation between circuits or lines. Therefore, microwave circuit packaging has necessarily been intricate and costly. In recent years, a microwave monolithic integrated circuit (abbreviated as MMIC hereinafter) is becoming gradually applied as a semiconductor integrated circuits in the high frequency band. However, the MMIC has many drawbacks. For example, it is generally easy to crack so that many packaging restrictions exist. In particular, it is not adapted to integration of distributed constant circuits which tend to result in large sizes.
Referring to FIG. 8 showing a packaging structure for a conventional microwave circuit including an MMIC, an MIC module 101 having a circuit element 103, microwave leads 102 and bias supply terminals 107 therein are arranged on a main plate 100. Here, the microwave leads 102 and the bias supply terminals 107 are led to the rear side of the main plate 100 by going through outer conductive holes 109 formed therein. The bias supply terminals 107 are soldered via a printed circuit board or the like, and the microwave leads 102 are electrically connected to another module or an isolator 108 by soldering via the printed circuit board 104. The connected parts of the microwave leads 102 are shielded by means of a cover 106 isolated from the outside.
As shown in FIG. 8, since the MMIC's are unsuitable for integration of a distributed constant circuit constituted mainly of passive elements, active elements are sealed in an airtight case and connection between these active elements and the outside passive elements is established by microstrip lines and by soldering. Therefore, the sealing of the MMIC into an airtight case is costly, and an intricate and expensive shielding case having finely compartmentalized small chambers is required to prevent undesirable electrical connection between unit circuits. Further, the cost for assembling runs high.
Accordingly, the above-mentioned conventional packaging structure has the following defects. (1) A considerable cost has to be spent for building in an MMIC into an airtight case called a header. This is because the header itself is expensive and the assembling cost is high also. (2) An intricate and large-sized shielding case which is subdivided into small chambers is costly. (3) All of fixing of the header to the shielding case, fitting of the printed circuit board, soldering of the terminals, or the like, have to be done manually which result in a high assembling cost. (4) The structure has a large size and a large weight, and it has been a hindrance to miniaturization and reduction in weight of communication equipment.